Printable Aligned Single-Walled Carbon Nanotube Film with Outstanding Thermal Conductivity and Electromagnetic Interference Shielding Performance

Highlights Ultrathin, lightweight, and ultraflexible aligned single-walled carbon nanotube (SWCNT) films were fabricated via a facile, environmentally friendly, and scalable printing methodology. The aligned pattern and outstanding intrinsic properties of SWCNTs rendered “metal-like” thermal conductivity, excellent mechanical strength, hydrophobicity, and remarkable electromagnetic interference (EMI) shielding performance of the films. The excellent EMI shielding stability and reliability when subjected to mechanical deformation, chemical corrosion, and extreme environments demonstrated the significant potential of the films in aerospace, defense, and smart wearable electronics. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-022-00883-9.


S1.1 Fabrication of Random Network SWCNT and MWCNT Buckypapers, and the Reduced Graphene Oxide (RGO) Films
The random network SWCNT Buckypapers were prepared by filtrating the as-prepared SWCNT dispersion with a cellulose membrane filter (0.22 μm pore size). DI water was employed to remove the surfactant. The resulting dried films were peeled off from the substrate cellulose membranes. In the same procedure, the different aspect-ratios MWCNT assembled Buckypapers were also prepared based on the commercial MWCNT aqueous dispersions (supplied by Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences): long MWCNT (TNM2, diameter around 8-15 nm and length around 50 μm) and short MWCNT (TNM8, average diameter around 50 nm and length 10-20 μm). The graphene films were prepared by the same vacuum filtration approach to the GO dispersion (prepared by a modified Hummer's method as reported in our previous work [23]) followed by a further reduction treatment by utilizing hydroiodic acid vapor as a reducing agent.

S1.2 Theoretical Simulation of SWCNT's Thermal Conductivity
To indicate the thermal conductivity ( ℎ ) theoretically, we calculated the lattice thermal conductivity by solving the phonon Boltzmann Transport Equation (BTE) with the firstprinciples simulations. The models we adopted are armchair SWCNTs (8,8) and (12,12), which are corresponding the diameter 1.085 and 1.6272 nm. Our simulating results of the lattice thermal conductivities along the axial direction at 300K are shown in Figure S5. ℎ of the SWCNT (8,8) is 3580 W m -1 K -1 , and ℎ of the SWCNT (12,12) is 3102 W m -1 K -1 . Our simulation results are consistent with other theoretical and experimental work [S1-S7]. Here, we only considered the ℎ along the axial direction along the SWCNTs.
Here is the details of the theory and simulating process. First, by solving the BTE, we have the following equation: S1) where and donate the phonon branch and wavevector respectively, ℎ is the specific heat capacity of phonon, is the phonon group velocity along the axial direction of SWCNTs and is the phonon lifetime. To obtain the key parameters and , we calculated the second and third order interatomic force constants (IFCs) based on the density functional theory (DFT) method. We performed all the first-principles calculations with the Vienna Ab-initio Simulation Package (VASP) [S8, S9], and chosen the Perdew-Burke-Ernzerhof (PBE) of the generalized gradient approximation (GGA) as the exchange correlation functional [S10]. We used the projector augmented wave (PAW) potentials to describe the core (1 2 ) and valence electrons (2 2 and 2 2 ) of carbon element. The kinetic energy cutoff of the wave functions was set as 500eV, which is enough for the hard-core carbon element. In the momentum space of electrons, the k-mesh 1×1×20 was used to sample the Brillouin Zone (BZ) including Γ point by Monkhorst-method. To hinder the self-interactions among the cylinders arising from the employed periodic boundary condition, we set a vacuum layer 10 Å among the neighbor unit cells. All the structures were fully optimized with the Hellmann-Feynman force tolerance 0.001 /Å . For the second and third order IFCs calculations, the supercell 1×1×6 was constructed, the convergence of length was examined. The second order harmonic IFCs were obtained under the linear response framework by using the finite displacement method as implemented in the PHONOPY package [S11]. The phonon dispersions can also be obtained from PHONOPY package, which is shown in Fig. S1. In the calculations of third order IFCs, the atomic force interaction cutoff was taken into account up to forth nearest neighbors. With the third order IFCs, we iteratively solved the phonon BTE by using ShengBTE code developed by Li et al. [S12]. The momentum space of phonon was sampled with 1×1×100 grid in first BZ. Then we have the phonon lifetime , and combining with the Eq. (1) we calculated the lattice thermal conductivity ℎ finally. The convergence of the sampling grid in momentum space for phonon was examined [S12]. To convert the ShengBTE results into the experimental values, we used the cross-sectional area = ℎ, for the SWCNTs [S13], where is the diameter and ℎ = 3.4 Å (the interactive length which is the van der Waals force radius of carbon atoms).

S1.3 Thermal Conductivity Measurement
Thermal conductivity of as-prepared freestanding SWCNT film was measured through our home-made vacuum thermal test apparatus (Fig. S6a). The as-prepared SWCNT films were cut into strips with width of around 5 mm and suspended in a vacuum chamber between two isolated stages, which were connected to alumel-chromel thermocouples. The two stages were named as floating and fixed stages, respectively. The floating stage was placed on Teflon tubes and did not make surface contact with anything other than the test sample. The fixed stage was connected to a power supply and could be warmed up by Joule heating. After loading sample, the apparatus was pumped down with a mechanical pump to reduce the chances of causing heat dissipation through convection. The thermal measurement was triggered by turning on the power supply attached to a heater on the fixed stage. The temperatures of the two stages were then recorded through the stage thermocouples every 60 seconds for thirty minutes, and the

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power supply was shut off for the final ten minutes. The thermal conductivity of the sample was calculated in between every two measured points using the following equations and then averaged together (Fig. S6b).
Here, is the mass of copper and stainless steel of the floating stage, is the heat capacity of the metals of the floating stage, is the temperature of fixed stage measured during test, is the temperature of floating stage measured during test, Rsample is the absolute thermal resistance of the sample, L is the thickness of the sample, which can be measured before test, A is the cross-sectional area perpendicular to the path of heat flow, is the thermal conductivity of the sample.
It can be found that we introduced a correction term ∆ compared to the standard heat equation. It is because the heat leaking from the floating stage, which should be proportional to the temperature difference between the floating stage and room temperature ambient, is nonnegligible. is an empirical constant that can be obtained through adjusted it until the thermal conductivity is close to a constant. For example, as shown in Figure S6c, the measured thermal conductivity of pure copper without leakage correction is displayed as blue squares, which shows an unreasonably non-constant feature. After introducing leakage correction, measured thermal conductivity of copper (red dots in Fig. S6c) became constant and close to its theoretical value. We also measured some pure metals (copper, aluminum and silver) and found their measured thermal conductivity values were consistent with their theoretical values (Fig. S6d).

S1.4 EMI Shielding Performance Test
The EMI shielding tests of the samples were carried out with the waveguide method by a vector network analyzer (VNA, Agilent 8517A). The tested samples were cut with size of 22.86×10.16 mm 2 (length × width) for the X-band frequency range of 8.2-12.4 GHz, 15.8×7.9 mm 2 (length × width) for the Ku-band frequency range of 12.4-18 GHz, and 5.68×2.84 mm 2 (length × width) for the Q-band frequency range of 33-50 GHz. Herein, the thin samples were fixed between two 1 mm-thick PC substrates with negligible EMI SE. In the Terahertz frequency range of 100-400 GHz, shielding performance was evaluated using terahertz time domain spectroscopy (Topical Teraflash). More than five samples for each component were tested. Unless specifically mentioned, the electric field direction of the incident EM waves was parallel to the aligned SWCNTs for the SWCNT films. The obtained S-parameters of each sample were used to calculate the EMI SE as follows: Where |Sij| 2 is the power transferred from port i to port j.

S1.5 Theoretical Calculation of EMI Shielding Performance
The complex transmission coefficient (T) of a homogeneous shield can be calculated by a Transfer Matrix Method. The continuity of the tangential parts of both electric and magnetic fields of a time harmonic (e jωt ) plane wave at the incident face of shields generate the boundary conditions: S9) where A and B are the coefficients of forward-travelling and backward-travelling waves, respectively, = √ is the wave number, = √ / is the admittance of shielding materials, and are the complex permeability and permittivity of shielding materials, the subscripts 0 and 1 are variables relating to the air and the shielding materials, respectively. Since our shielding architectures are nonmagnetic, equals to 1. The complex permittivity ( ) consist of the real part ( ') and imaginary part ( '')as following: where w is the angular frequency and σ is the conductivity. Herein, for a conductivity-caused EMI shielding calculation of the homogenous shields, the real part ( ') is equal to 0 .
Thus, the boundary condition gives as follows at the wave emergent face of the shielding materials: The T of the shielding materials are calculated as follows:

S2 Supplementary Videos
Video S1 The printing process for preparing the SWNCT film